Many types of envelope structures are, in general, well known. A common disadvantage of many envelope structures is that they can only be used once and are then usually discarded afterwards thereby creating unnecessary waste after a single use. Some envelopes fail to be used even once before being discarded. Moreover, it is common for an otherwise unused envelope structure to be discarded because it has been preaddressed for a particular recipient. For example, certain envelope structures are frequently utilized for mailing invoices and the like. A second envelope, which is often preaddressed and sometimes provided with postage, is usually included with the invoice for returning the invoice to the sender. In the case where the invoice is not returned, such as where a payment or correspondence is made electronically, the second preaddressed envelope is usually discarded. This practice, although not uncommon, is unfortunately wasteful, especially in large volumes. Thus, easily reusable envelope structures are desirable.
Envelopes have been developed that utilize a single structure to form primary and return envelopes such as are described in U.S. Pat. No. 4,194,631 to Rangan and U.S. Pat. No. 4,715,531 to Stewart et al. These envelopes are directed to small envelopes such as conventional #10 envelopes. Envelopes of this type are convertible from a primary to a return envelope. That is, tearing and folding steps are used to convert a received envelope to an envelope that can be returned to the sender or forwarded to another party. Typically, these structures are quite complex and somewhat costly to produce. Thus, reusable envelopes in general have been limited small envelopes and large established markets for their use.
Additionally, known reusable envelope structures can be somewhat difficult to utilize because of a requirement for performing complex operations in order to manipulate the envelope. That is, a cumbersome sequence of steps must be followed in order to convert the envelope. Moreover, many envelopes of this type commonly include tags, glue patches, or loose edges being left on the envelope, which can interfere with machine sorting equipment, especially on the return trip. As such, easy to use and cost effective reusable envelope structures are desirable, especially for large envelopes.